#[cfg(test)]
mod tests {
    #[test]
    fn iter_d() {
        let v1 = vec![1, 2, 3];
        let mut v1_iter = v1.iter();
        assert_eq!(v1_iter.next(), Some(&1));
        assert_eq!(v1_iter.next(), Some(&2));
        assert_eq!(v1_iter.next(), Some(&3));
        assert_eq!(v1_iter.next(), None);
    }

    #[test]
    fn iter_sum() {
        let v1 = vec![1, 2, 3];
        let v1_iter = v1.iter();
        let total: i32 = v1_iter.sum();
        assert_eq!(total, 6);
    }
}
